Multiple vapor feeds for hydrogenation process to produce alcohol

ABSTRACT

The present invention relates to processes for the recovery of ethanol from a crude ethanol product obtained from the hydrogenation of acetic acid. The crude ethanol product is separated in a column to produce a distillate stream comprising ethyl acetate, ethanol and acetaldehyde and a residue stream comprising ethanol, acetic acid and water. The ethanol product is recovered from the residue stream. A liquid recycle stream is sent to a second vaporizer to form a second vapor feed stream that is fed to the hydrogenation reactor.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Prov. App. No. 61/576,195, filed on Dec. 15, 2011, the entire contents and disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producing alcohol and, in particular, to a process for using multiple vapor feeds for the hydrogenation process to produce ethanol. In one embodiment, the process uses multiple vaporizers to convert fresh liquid acetic acid into a vapor stream and separately to convert recycled liquid into a vapor stream.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feed stocks, such as petroleum oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulosic materials, such as corn or sugar cane. Conventional methods for producing ethanol from organic feed stocks, as well as from cellulosic materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in organic feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulosic materials, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulosic materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acids, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. These impurities limit the production and recovery of ethanol from such reaction mixtures. For example, during hydrogenation, esters are produced that together with ethanol and/or water form azeotropes, which are difficult to separate. In addition, when conversion is incomplete, acid remains in the crude ethanol product, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanol involving converting the hydrocarbons to ethanoic acid and hydrogenating the ethanoic acid to ethanol. The stream from the hydrogenation reactor is separated to obtain an ethanol stream and a stream of acetic acid and ethyl acetate, which is recycled to the hydrogenation reactor.

U.S. Pat. No. 7,842,844 describes a process for improving selectivity and catalyst activity and operating life for the conversion of hydrocarbons to ethanol and optionally acetic acid in the presence of a particulate catalyst, said conversion proceeding via a syngas generation intermediate step.

The need remains for improved processes for recovering ethanol from a crude product obtained by reducing alkanoic acids, such as acetic acid, and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a process for producing ethanol comprising vaporizing an acetic acid stream in a first vaporizer to form a first feed stream, reacting the first feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product, which may comprise ethanol and ethyl acetate, separating at least a portion of the crude ethanol product in one or more columns, preferably two or more columns, to produce ethanol and a liquid recycle stream. The liquid recycle stream may comprise ethyl acetate, ethanol and acetaldehyde. In one embodiment the liquid recycle stream is substantially free of acetic acid, e.g., may comprise less than 600 wppm acetic acid. The process further comprises vaporizing the liquid recycle stream in a second vaporizer, which is preferably different than the first vaporizer, to form a second feed stream that is fed to the at least one reactor. In one embodiment, the first feed stream is fed to the at least one reactor separately from the second feed stream and the first feed stream is not mixed or contacted with second feed stream prior to the at least one reactor. Advantageously this reduces the esterification reactions in the first feed stream prior to the at least one reactor and may maximize the amount of acetic acid that is passed over the catalyst.

To form the first feed stream, fresh acetic acid and hydrogen, preferably fresh hydrogen, may be fed to the first vaporizer. Hydrogen may also be fed to the second vaporizer, and in some embodiments, recycled hydrogen may be fed to the second vaporizer. As used through the application, fresh refers to reactants that have not be passed over the catalyst and recycled refers to reactants that have been passed over the catalyst, or products from the crude ethanol product that are returned to the at least one reactor.

In one embodiment, the first vaporizer may be construed of a corrosion resistance material and may operate at a temperature from 20° C. to 300° C. and a pressure of 10 kPa to 3000 kPa. The second vaporizer may operate at a similar temperature and/or pressure, but is preferably construed of a material that is different than the first vaporizer. The material does not need to be corrosion resistant for the second vaporizer because acetic acid, either fresh or recycled, is not fed to the second vaporizer.

In a second embodiment, the present invention is directed to a process for producing ethanol, comprising vaporizing an acetic acid stream in a first vaporizer to form a first feed stream, reacting the first feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product, separating at least a portion of the crude ethanol product in a first distillation column to yield a first residue comprising acetic acid and a first distillate comprising ethanol, ethyl acetate, and water, separating a portion of the first distillate in the second distillation column to yield a second residue comprising ethanol and water and a second distillate comprising ethyl acetate, and vaporizing the second distillate in a second vaporizer to form a second feed stream that is fed to the at least one reactor. In one embodiment, the first feed stream is fed to the at least one reactor separately from the second feed stream and the first feed stream is not mixed or contacted with second feed stream prior to the at least one reactor. In one embodiment, the acetic acid from the first residue may be recycled to the first vaporizer.

In a third embodiment, the present invention is directed to a process for producing ethanol, comprising vaporizing an acetic acid stream in a first vaporizer to form a first feed stream, reacting the first feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product, separating at least a portion of the crude ethanol product in a first distillation column to yield a first residue comprising acetic acid and a first distillate comprising ethanol, ethyl acetate, and water, removing water from at least a portion of the first distillate to yield an ethanol mixture stream comprising less than 10 wt. % water, separating a portion of the ethanol mixture stream in a second distillation column to yield a second residue comprising ethanol and a second distillate comprising ethyl acetate, and vaporizing the second distillate in a second vaporizer to form a second feed stream that is fed to the at least one reactor. In one embodiment, the first feed stream is fed to the at least one reactor separately from the second feed stream and the first feed stream is not mixed or contacted with second feed stream prior to the at least one reactor. In one embodiment, the acetic acid from the first residue, after optionally separating water, may be recycled to the first vaporizer.

In a fourth embodiment, the present invention is directed to a process for producing ethanol, comprising vaporizing an acetic acid stream in a first vaporizer to form a first feed stream, reacting the first feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product, separating a portion of the crude ethanol product in a first distillation column to yield a first distillate comprising ethyl acetate and acetaldehyde, and a first residue comprising ethanol, acetic acid, water or mixtures thereof, and separating a portion of the first residue in a second distillation column to yield a second residue comprising acetic acid and water and a second distillate comprising ethanol and ethyl acetate. In one embodiment, ethanol is recovered from the first residue, and thus the mixture preferably comprises ethanol and either acetic acid and water. The first residue may also comprise ethyl acetate. The process further comprises separating a portion of the second distillate in a third distillation column to yield a third residue comprising ethanol and a third distillate comprising ethyl acetate. In one embodiment, prior to the third distillation column, water may be removed using a water removal unit, such as a pressure swing adsorption, mole sieve, or membrane. The process further comprises vaporizing at least one of the first distillate or third distillate in a second vaporizer to form a second feed stream that is fed to the at least one reactor. In one embodiment, the first feed stream is fed to the at least one reactor separately from the second feed stream, and the first feed stream is not mixed or contacted with second feed stream prior to the at least one reactor. In one embodiment, the acetic acid from the second residue, after optionally separating water, may be recycled to the first vaporizer. In one embodiment, an extractive agent, such as water, may be fed to the first distillation column.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of a hydrogenation process in accordance with an embodiment of the present invention.

FIG. 2 is a schematic diagram of another hydrogenation process in accordance with an embodiment of the present invention.

FIG. 3 is a schematic diagram of yet another hydrogenation process in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for producing ethanol from multiple vapor feed streams in the presence of a catalyst. Preferably, there are at least two vapor feed streams having different compositions. In one embodiment, at least one of the vapor feed streams comprises fresh acetic acid. Fresh acetic acid refers to acetic acid that has not been passed over a hydrogenation catalyst. While one vapor feed stream may comprise fresh acetic acid, the other vapor feed stream may contain substantially no fresh acetic acid.

The hydrogenation reaction produces a crude ethanol product, depending on acetic acid conversion, may comprise ethanol, water, ethyl acetate, acetaldehyde, acetic acid, or other impurities. The processes of the present invention involve separating the crude ethanol product in one or more columns, preferably two or more columns, to produce ethanol and a liquid recycle stream comprising ethyl acetate, acetaldehyde, ethanol or mixtures thereof. In one embodiment, the liquid recycle stream may be vaporized to yield a second vapor feed stream. The liquid recycle stream preferably comprises ethyl acetate and is substantially free of acetic acid. The liquid recycle stream may also comprise mixtures of acetaldehyde, diethyl acetal, ethanol, and/or water. In some optional embodiment, the liquid feed stream may have a reduced amount of acetic acid, e.g., less than 600 wppm acetic acid. Stated otherwise, because the liquid feed stream does not contain acetic acid or has low amounts of acetic acid, no acetic acid may be recycled from the separation zone.

In one embodiment, the catalyst for hydrogenating acetic acid may also be capable of converting ethyl acetate to ethanol. Generally the catalysts may convert more acetic acid than ethyl acetate. This allows for a liquid recycle of at least a portion of the ethyl acetate produced by hydrogenating acetic acid. When the liquid recycle stream is contacted with the fresh acetic acid, due to the composition of the liquid recycle stream and to the esterification equilibrium, some of the fresh acetic acid may be converted to ethyl acetate. Without being bound by theory, the fresh acetic acid may be converted due to the ethanol concentration in the liquid recycle stream. This reduces the total amount of fresh acetic acid fed to the at least one reactor and may increase the ethyl acetate fed to the at least one reactor. To minimize the amount of ethyl acetate formed, the liquid recycle stream is converted to a vapor feed stream in a separate vaporizer than the fresh acetic acid. Each vapor feed stream may be produced by separate vaporizers. The metallurgy for the vaporizer for the liquid recycle stream does not need to be corrosive resistant due to the relatively low concentrations of acetic acid.

In one embodiment, one vaporizer has a concentration of acetic acid that is greater than the other vaporizers. Thus, at least one vaporizer has a concentration of acetic acid that is greater than 50 mol. %, e.g., greater than 75 mol. %. The other vaporizers may be substantially free of acetic acid. In another embodiment, one vaporizer may have a greater concentration of ethyl acetate than the vaporizer that contains fresh acetic acid. At least one vaporizer, preferably that does not contain fresh acetic acid, and has a concentration of ethyl acetate that is greater than 15 mol. %, e.g. greater than 30 mol. %.

Each of the vapor feed streams produced by the vaporizers are separately introduced into the reactor and not mixed or contacted prior to being introduced into the reactor. The vapor stream comprising the fresh acetic acid may have a relative mass flow that is greater than the mass flow of the other vapor streams. For example the relative mass flow of the vapor stream comprising the fresh acetic acid may be at least 2 times greater, e.g., at least 5 times greater or at least 10 times greater, than the total mass flow of the other vapor feed streams.

The temperature of the feed stream containing fresh acetic acid may be from 100° C. to 350° C., e.g., from 120° C. to 310° C. or from 150° C. to 300° C. The temperature of the other vapor feed stream may be from 50° C. to 350° C., e.g., from 70° C. to 310° C. or from 100° C. to 300° C.

Using multiple vaporizers may also allow for efficient scaling and the ethanol production capacity to increase. Hydrogen may be fed to each vaporizer as necessary. Preferably hydrogen should at least be introduced into the vaporizer that converts fresh acetic acid to a vapor stream.

In recovering ethanol, the processes of the present invention may use two or more distillation columns. In one embodiment, a first distillation column is used to separate the crude ethanol stream into a residue stream comprising acetic acid. Depending on what the ethanol concentration is, either in the distillate or residue, the stream containing the ethanol from the first distillation column may be subsequently separated to obtain ethanol. The remaining streams may be returned to the vaporizer as the liquid recycle streams. There may be at least one liquid recycle stream that comprises ethyl acetate from this separation.

In another embodiment, a first distillation column is used to separate the feed stream into a residue stream comprising water and acetic acid from the crude ethanol product and a distillate stream comprising ethanol, acetaldehyde and ethyl acetate. The residue may comprise a substantial portion of the water. In one embodiment, 30 to 90% of the water in the crude ethanol product is removed in the residue, e.g., from 40 to 88% of the water or from 50 to 84% of the water. Water may also be removed from the distillate to form an ethanol mixture stream, preferably comprising less than 10 wt. % water, less than 6 wt. % water or less than 4 wt. % water. In terms of ranges the ethanol mixture stream comprises from 0.001 to 10 wt. % water, e.g., from 0.01 to 6 wt. % water or from 0.1 to 4 wt. % water. Water may be removed, for example, using an adsorption unit, membrane, molecular sieves, extractive column distillation, or a combination thereof. Suitable adsorption units include pressure swing adsorption (PSA) units and thermal swing adsorption (TSA) units. The adsorption units may comprise molecular sieves, such as aluminosilicate compounds. Product ethanol is then recovered from the ethanol mixture stream. There may be at least one liquid recycle stream that comprises ethyl acetate that is also recovered from the ethanol mixture stream.

In another embodiment, a first distillation column is used to separate the crude stream into a residue stream comprising ethanol, water, acetic acid or mixtures thereof, and a distillate stream comprising acetaldehyde, ethanol and ethyl acetate. The distillate may be the liquid recycle stream. The residue stream, for example, may comprise at least 50% of the ethanol from the crude ethanol product, and more preferably at least 70%. In terms of ranges, the residue stream may comprise from 50% to 99.9% of the ethanol from the crude ethanol product, and more preferably from 70% to 99%. Preferably, the amount of ethanol from the crude ethanol recovered in the residue may be greater than 97.5%, e.g. greater than 99.9%.

The residue may also comprise a substantial portion of the water and acetic acid from the crude ethanol product. The residue stream comprising ethanol, ethyl acetate, water, and acetic acid may be further separated to recover ethanol. Because these compounds may not be in equilibrium, additional ethyl acetate may be produced through esterification of ethanol and acetic acid. In one preferred embodiment, the water and acetic acid may be removed as another residue stream in a separate distillation column. In addition, the water carried over in the separate distillation column may be removed with a water separator that is selected from the group consisting of an adsorption unit, membrane, extractive column distillation, molecular sieves, and combinations thereof.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenation process for producing ethanol. The materials, catalysts, reaction conditions, and separation processes that may be used in the hydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with the process of this invention may be derived from any suitable source including natural gas, petroleum, coal, biomass, and so forth. As examples, acetic acid may be produced via methanol carbonylation, acetaldehyde oxidation, ethane oxidation, oxidative fermentation, and anaerobic fermentation. Methanol carbonylation processes suitable for production of acetic acid are described in U.S. Pat. Nos. 7,208,624; 7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976; 5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosures of which are incorporated herein by reference. Optionally, the production of ethanol may be integrated with such methanol carbonylation processes.

As petroleum and natural gas prices fluctuate becoming either more or less expensive, methods for producing acetic acid and intermediates such as methanol and carbon monoxide from alternate carbon sources have drawn increasing interest. In particular, when petroleum is relatively expensive, it may become advantageous to produce acetic acid from synthesis gas (“syngas”) that is derived from other available carbon source. U.S. Pat. No. 6,232,352, the entirety of which is incorporated herein by reference, for example, teaches a method of retrofitting a methanol plant for the manufacture of acetic acid. By retrofitting a methanol plant, the large capital costs associated with CO generation for a new acetic acid plant are significantly reduced or largely eliminated. All or part of the syngas is diverted from the methanol synthesis loop and supplied to a separator unit to recover CO, which is then used to produce acetic acid. In a similar manner, hydrogen for the hydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for the above-described acetic acid hydrogenation process may be derived partially or entirely from syngas. For example, the acetic acid may be formed from methanol and carbon monoxide, both of which may be derived from syngas. The syngas may be formed by partial oxidation reforming or steam reforming, and the carbon monoxide may be separated from syngas. Similarly, hydrogen that is used in the step of hydrogenating the acetic acid to form the crude ethanol product may be separated from syngas. The syngas, in turn, may be derived from variety of carbon sources. The carbon source, for example, may be selected from the group consisting of natural gas, oil, petroleum, coal, biomass, and combinations thereof. Syngas or hydrogen may also be obtained from bio-derived methane gas, such as bio-derived methane gas produced by landfills or agricultural waste.

Biomass-derived syngas has a detectable ¹⁴C isotope content as compared to fossil fuels such as coal or natural gas. An equilibrium forms in the Earth's atmosphere between constant new formation and constant degradation, and so the proportion of the ¹⁴C nuclei in the carbon in the atmosphere on Earth is constant over long periods. The same distribution ratio n¹⁴C:n¹²C ratio is established in living organisms as is present in the surrounding atmosphere, which stops at death and ¹⁴C decomposes at a half life of about 6000 years. Methanol, acetic acid and/or ethanol formed from biomass-derived syngas would be expected to have a ¹⁴C content that is substantially similar to living organisms. For example, the ¹⁴C:¹²C ratio of the methanol, acetic acid and/or ethanol may be from one half to about 1 of the ¹⁴C:¹²C ratio for living organisms. In other embodiments, the syngas, methanol, acetic acid and/or ethanol described herein are derived wholly from fossil fuels, i.e. carbon sources produced over 60,000 years ago, may have no detectable ¹⁴C content.

In another embodiment, the acetic acid used in the hydrogenation step may be formed from the fermentation of biomass. The fermentation process preferably utilizes an acetogenic process or a homoacetogenic microorganism to ferment sugars to acetic acid producing little, if any, carbon dioxide as a by-product. The carbon efficiency for the fermentation process preferably is greater than 70%, greater than 80% or greater than 90% as compared to conventional yeast processing, which typically has a carbon efficiency of about 67%. Optionally, the microorganism employed in the fermentation process is of a genus selected from the group consisting of Clostridium, Lactobacillus, Moorella, Thermoanaerobacter, Propionibacterium, Propionispera, Anaerobiospirillum, and Bacteriodes, and in particular, species selected from the group consisting of Clostridium formicoaceticum, Clostridium butyricum, Moorella thermoacetica, Thermoanaerobacter kivui, Lactobacillus delbrukii, Propionibacterium acidipropionici, Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodes amylophilus and Bacteriodes ruminicola. Optionally in this process, all or a portion of the unfermented residue from the biomass, e.g., lignans, may be gasified to form hydrogen that may be used in the hydrogenation step of the present invention. Exemplary fermentation processes for forming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180; 6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and 7,888,082, the entireties of which are incorporated herein by reference. See also US Publ. Nos. 2008/0193989 and 2009/0281354, the entireties of which are incorporated herein by reference.

Examples of biomass include, but are not limited to, agricultural wastes, forest products, grasses, and other cellulosic material, timber harvesting residues, softwood chips, hardwood chips, tree branches, tree stumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover, wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus, animal manure, municipal garbage, municipal sewage, commercial waste, grape pumice, almond shells, pecan shells, coconut shells, coffee grounds, grass pellets, hay pellets, wood pellets, cardboard, paper, plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety of which is incorporated herein by reference. Another biomass source is black liquor, a thick, dark liquid that is a byproduct of the Kraft process for transforming wood into pulp, which is then dried to make paper. Black liquor is an aqueous solution of lignin residues, hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, provides a method for the production of methanol by converting carbonaceous materials such as oil, coal, natural gas and biomass materials. The process includes hydrogasification of solid and/or liquid carbonaceous materials to obtain a process gas which is steam pyrolized with additional natural gas to form syngas. The syngas is converted to methanol which may be carbonylated to acetic acid. The method likewise produces hydrogen which may be used in connection with this invention as noted above. U.S. Pat. No. 5,821,111, which discloses a process for converting waste biomass through gasification into syngas, and U.S. Pat. No. 6,685,754, which discloses a method for the production of a hydrogen-containing gas composition, such as a syngas including hydrogen and carbon monoxide, are incorporated herein by reference in their entireties.

Acetic acid fed to the hydrogenation reaction may also comprise other carboxylic acids and anhydrides, as well as acetaldehyde and acetone. Generally ethyl acetate may be recovered from the liquid recycle streams when recovering ethanol. Preferably, a suitable acetic acid feed stream comprises one or more of the compounds selected from the group consisting of acetic acid, acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof. Acetic acid is the primary component in the acetic acid feed stream. The other compounds may also be hydrogenated in the processes of the present invention. In some embodiments, the presence of carboxylic acids, such as propanoic acid or its anhydride, may be beneficial in producing propanol. Water may also be present in the acetic acid feed and/or the liquid recycle streams.

Alternatively, acetic acid in vapor form may be taken directly as crude product from the flash vessel of a methanol carbonylation unit of the class described in U.S. Pat. No. 6,657,078, the entirety of which is incorporated herein by reference. The crude vapor product, for example, may be fed directly to the ethanol synthesis reaction zones of the present invention without the need for condensing the acetic acid and light ends or removing water, saving overall processing costs.

Some embodiments of the process of hydrogenating acetic acid to form ethanol may include a variety of configurations using a fixed bed reactor or a fluidized bed reactor. In many embodiments of the present invention, an “adiabatic” reactor can be used; that is, there is little or no need for internal plumbing through the reaction zone to add or remove heat. In other embodiments, a radial flow reactor or reactors may be employed, or a series of reactors may be employed with or without heat exchange, quenching, or introduction of additional feed material. Alternatively, a shell and tube reactor provided with a heat transfer medium may be used. In many cases, the reaction zone may be housed in a single vessel or in a series of vessels with heat exchangers therebetween.

In preferred embodiments, the catalyst is employed in a fixed bed reactor, e.g., in the shape of a pipe or tube, where the reactants, typically in the vapor form, are passed over or through the catalyst. Other reactors, such as fluid or ebullient bed reactors, can be employed. In some instances, the hydrogenation catalysts may be used in conjunction with an inert material to regulate the pressure drop of the reactant stream through the catalyst bed and the contact time of the reactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phase or vapor phase. Preferably, the reaction is carried out in the vapor phase under the following conditions. The reaction temperature may range from 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to 300° C., or from 250° C. to 300° C. The reactor pressure may range from 100 kPa to 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 2100 kPa. The reactants may be fed to the reactor at a gas hourly space velocity (GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greater than 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms of ranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure just sufficient to overcome the pressure drop across the catalytic bed at the GHSV selected, although there is no bar to the use of higher pressures, it being understood that considerable pressure drop through the reactor bed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or 6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of acetic acid to produce one mole of ethanol, the actual molar ratio of hydrogen to acetic acid in the feed stream may vary from about 100:1 to 1:100, e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 18:1 to 2:1. Most preferably, the molar ratio of hydrogen to acetic acid is greater than 2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon such variables as amount of acetic acid, catalyst, reactor, temperature, and pressure. Typical contact times range from a fraction of a second to more than several hours when a catalyst system other than a fixed bed is used, with preferred contact times, at least for vapor phase reactions, from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to 30 seconds.

The hydrogenation of acetic acid and ethyl acetate to form ethanol is preferably conducted in the presence of a hydrogenation catalyst. Preferably, the hydrogenation catalyst is capable of converting both acetic acid and ethyl acetate. Suitable hydrogenation catalysts include catalysts comprising a first metal and optionally one or more of a second metal, a third metal or any number of additional metals, optionally on a catalyst support. Preferred bimetallic combinations for some exemplary catalyst compositions include platinum/tin, platinum/ruthenium, platinum/rhenium, palladium/ruthenium, palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin, silver/palladium, copper/palladium, copper/zinc, nickel/palladium, gold/palladium, ruthenium/rhenium, and ruthenium/iron. Additional metal combinations may include palladium/rhenium/tin, palladium/rhenium/cobalt, palladium/rhenium/nickel, platinum/tin/palladium, platinum/tin/cobalt, platinum/tin/copper, platinum/tin/chromium, platinum/tin/zinc, and platinum/tin/nickel.

The hydrogenation of acetic acid to form ethanol is preferably conducted in the presence of a hydrogenation catalyst. Exemplary catalysts are further described in U.S. Pat. Nos. 7,608,744 and 7,863,489, and U.S. Pub. Nos. 2010/0121114 and 2010/0197985, the entireties of which are incorporated herein by reference. In another embodiment, the catalyst comprises a Co/Mo/S catalyst of the type described in U.S. Pub. No. 2009/0069609, the entirety of which is incorporated herein by reference. In some embodiments the catalyst may be a bulk catalyst.

In one embodiment, the catalyst comprises a first metal selected from the group consisting of copper, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium, rhenium, molybdenum, and tungsten. Preferably, the first metal is selected from the group consisting of platinum, palladium, cobalt, nickel, and ruthenium. More preferably, the first metal is selected from platinum and palladium. In embodiments of the invention where the first metal comprises platinum, it is preferred that the catalyst comprises platinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or less than 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprises a second metal, which typically would function as a promoter. If present, the second metal preferably is selected from the group consisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium, tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium, rhenium, gold, and nickel. More preferably, the second metal is selected from the group consisting of copper, tin, cobalt, rhenium, and nickel. More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals, e.g., a first metal and a second metal, the first metal is present in the catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt. %, or from 0.1 to 3 wt. %. The second metal preferably is present in an amount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 7.5 wt. %. For catalysts comprising two or more metals, the two or more metals may be alloyed with one another or may comprise a non-alloyed metal solution or mixture.

The catalyst may also comprise a third metal selected from any of the metals listed above in connection with the first or second metal, so long as the third metal is different from the first and second metals. In preferred aspects, the third metal is selected from the group consisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin, and rhenium. More preferably, the third metal is selected from cobalt, palladium, and ruthenium. When present, the total weight of the third metal preferably is from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 7.5 wt. %. In one embodiment, the catalyst may comprise platinum, tin and cobalt.

In addition to one or more metals, in some embodiments of the present invention the catalysts further comprise a support or a modified support. As used herein, the term “modified support” refers to a support that includes a support material and a support modifier, which adjusts the acidity of the support material.

The total weight of the support or modified support, based on the total weight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from 78 to 99 wt. %, or from 80 to 97.5 wt. %. In preferred embodiments that utilize a modified support, the support modifier is present in an amount from 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 1 to 20 wt. %, or from 3 to 15 wt. %, based on the total weight of the catalyst. The metals of the catalysts may be dispersed throughout the support, layered throughout the support, coated on the outer surface of the support (i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, support materials are selected such that the catalyst system is suitably active, selective and robust under the process conditions employed for the formation of ethanol.

Suitable support materials may include, for example, stable metal oxide-based supports or ceramic-based supports. Preferred supports include silicaceous supports, such as silica, silica gel, silica/alumina, a Group IIA silicate such as calcium metasilicate, pyrogenic silica, high purity silica, and mixtures thereof. Other supports may include, but are not limited to, iron oxide, alumina, titania, zirconia, magnesium oxide, carbon, graphite, high surface area graphitized carbon, activated carbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a support modifier. In some embodiments, the support modifier may be an acidic modifier that increases the acidity of the catalyst. Suitable acidic support modifiers may be selected from the group consisting of: oxides of Group IVB metals, oxides of Group VB metals, oxides of Group VIB metals, oxides of Group VIIB metals, oxides of Group VIIIB metals, aluminum oxides, and mixtures thereof. Acidic support modifiers include those selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers include those selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, and Al₂O₃. The acidic modifier may also include selected from the group consisting of WO₃, MoO₃, Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier that has a low volatility or no volatility. Such basic modifiers, for example, may be selected from the group consisting of: (i) alkaline earth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metal metasilicates, (iv) alkali metal metasilicates, (v) Group IIB metal oxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metal oxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. In addition to oxides and metasilicates, other types of modifiers including nitrates, nitrites, acetates, and lactates may be used. Preferably, the support modifier is selected from the group consisting of oxides and metasilicates of any of sodium, potassium, magnesium, calcium, scandium, yttrium, and zinc, as well as mixtures of any of the foregoing. More preferably, the basic support modifier is a calcium silicate, and even more preferably calcium metasilicate (CaSiO₃). If the basic support modifier comprises calcium metasilicate, it is preferred that at least a portion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA) Silica Catalyst Carrier from Saint Gobain N or Pro. The Saint-Gobain N or Pro SS61138 silica exhibits the following properties: contains approximately 95 wt. % high surface area silica; surface area of about 250 m²/g; median pore diameter of about 12 nm; average pore volume of about 1.0 cm³/g as measured by mercury intrusion porosimetry and a packing density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheres from Sud Chemie having a nominal diameter of about 5 mm, a density of about 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, a surface area of about 160 to 175 m²/g, and a pore volume of about 0.68 ml/g.

The catalyst compositions suitable for use with the present invention preferably are formed through metal impregnation of the modified support, although other processes such as chemical vapor deposition may also be employed. Such impregnation techniques are described in U.S. Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197985 referred to above, the entireties of which are incorporated herein by reference.

After the washing, drying and calcining of the catalyst is completed, the catalyst may be reduced in order to activate the catalyst. Reduction is carried out in the presence of a reducing gas, preferably hydrogen. The reducing gas is continuously passed over the catalyst at an initial ambient temperature that is increased up to 400° C. In one embodiment, the reduction is preferably carried out after the catalyst has been loaded into the reaction vessel where the hydrogenation will be carried out.

In particular, the hydrogenation of acetic acid may achieve favorable conversion of acetic acid and favorable selectivity and productivity to ethanol. For purposes of the present invention, the term “conversion” refers to the amount of acetic acid in the feed that is converted to a compound other than acetic acid. Conversion is expressed as a percentage based on acetic acid in the feed. The conversion may be at least 40%, e.g., at least 50%, at least 60%, at least 70% or at least 80%. Although catalysts that have high conversions are desirable, such as at least 80% or at least 90%, in some embodiments a low conversion may be acceptable at high selectivity for ethanol.

Selectivity is expressed as a mole percent based on converted acetic acid. It should be understood that each compound converted from acetic acid has an independent selectivity and that selectivity is independent from conversion. For example, if 60 mole % of the converted acetic acid is converted to ethanol, we refer to the ethanol selectivity as 60%. Preferably, the catalyst selectivity to ethanol is at least 60%, e.g., at least 70%, or at least 80%. Preferred embodiments of the hydrogenation process also have low selectivity to undesirable products, such as methane, ethane, and carbon dioxide. The selectivity to these undesirable products preferably is less than 4%, e.g., less than 2% or less than 1%.

The term “productivity,” as used herein, refers to the grams of a specified product, e.g., ethanol, formed during the hydrogenation based on the kilograms of catalyst used per hour. The productivity may range from 100 to 3,000 grams of ethanol per kilogram of catalyst per hour.

In various embodiments of the present invention, the crude ethanol stream produced by the hydrogenation process, before any subsequent processing, such as purification and separation, will typically comprise acetic acid, ethanol and water. Exemplary compositional ranges for the crude ethanol product are provided in Table 1, excluding hydrogen. The “others” identified in Table 1 may include, for example, esters, ethers, aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc. Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 72 15 to 72 15 to 70 25 to 65 Acetic Acid 0 to 90  0 to 50  0 to 35  0 to 15 Water 5 to 40  5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30  1 to 25  3 to 20  5 to 18 Acetaldehyde 0 to 10 0 to 3 0.1 to 3   0.2 to 2   Others 0.1 to 10   0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product comprises acetic acid in an amount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. % or less than 5 wt. %. In terms of ranges, the acetic acid concentration of Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.2 wt. % to 15 wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt. %. In embodiments having lower amounts of acetic acid, the conversion of acetic acid is preferably greater than 75%, e.g., greater than 85% or greater than 90%. In addition, the selectivity to ethanol may also be preferably high, and is preferably greater than 75%, e.g., greater than 85% or greater than 90%.

Ethanol Separation

Ethanol produced by the reactor may be recovered using several different techniques. In FIG. 1, the separation of the crude ethanol product uses four columns. In FIG. 2, the crude ethanol product is separated in two columns with an intervening water separation. In FIG. 3, the separation of the crude ethanol product uses three columns. Other separation systems may also be used with embodiments of the present invention.

Hydrogenation system 100 includes a reaction zone 101 and separation zone 102. Hydrogen and acetic acid via lines 104 and 105, respectively, are fed to a first vaporizer 106 to create a first vapor feed stream in line 107 that is directed to reactor 108. Hydrogen feed line 105 may be preheated to a temperature from 30° C. to 150° C., e.g., from 50° C. to 125° C. or from 60° C. to 115° C. Hydrogen feed line 104 may be fed at a pressure similar to the reactor pressure, such as from 10 kPa to 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 2100 kPa. Acetic acid in line 105 comprises fresh acetic acid. In one embodiment, lines 104 and 105 may be combined and jointly fed to first vaporizer 106. The temperature of the first feed stream in line 107 is preferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. or from 150° C. to 300° C. Any feed that is not vaporized is removed from first vaporizer 106 in blowdown stream 115 and may be recycled or discarded thereto. The mass ratio of first feed stream in line 107 to blowdown stream 115 may be from 6:1 to 500:1, e.g., from 10:1 to 500:1, from 20:1 to 500:1 or from 50:1 to 500:1. In addition, although first vapor feed stream in line 107 is shown as being directed to the top of reactor 108, line 107 may be directed to the side, upper portion, or bottom of reactor 108.

As shown in FIGS. 1 to 3, there is also a second vaporizer 113 for converting a liquid recycle stream from separation zone 102. A liquid recycle stream from separation zone 102 may be fed to second vaporizer 113 to form a second feed stream in line 118 that is directed to reactor 108. The temperature of the second feed stream in line 118 is preferably from 50° C. to 350° C., e.g., from 70° C. to 310° C. or from 100° C. to 300° C. Although not limited, the second feed stream temperature may be less than the first feed stream temperature. In one embodiment, second feed stream in line 118 and first feed stream in line 107 are fed separately to reactor 108. Preferably, second feed stream in line 118 is not mixed with the first feed stream in line 107 prior to being introduced to reactor 108.

A portion of the hydrogen in line 104 may optionally be fed to second vaporizer 113 via line 114. In some further embodiments, fresh hydrogen in line 104 may be introduced to first vaporizer 106 and recycled hydrogen from a portion of vapor stream 111 may be introduced into second vaporizer 113.

Any feed that is not vaporized is removed from vaporizer 113 in blowdown stream 116 and may be recycled or discarded thereto. The mass ratio of second feed stream in line 118 to blowdown stream 116 may be from 6:1 to 500:1, e.g., from 10:1 to 500:1, from 20:1 to 500:1 or from 50:1 to 500:1. In some embodiments, blowdown stream 116 may pass through first vaporizer 106 and the heavy components are discarded in blowdown stream 115.

The liquid recycle stream from separation zone 102 comprises ethyl acetate, ethanol, acetaldehyde and a reduced amount of acetic acid, e.g., less than 600 wppm or substantially free of acetic acid. This reduced amount of acetic acid allows for second vaporized 113 to be conducted from a different material than first vaporizer 106. First vaporizer 106 may be constructed from a corrosion resistant material due to the corrosive nature of acetic acid. However, second vaporizer 113 does not require such a corrosion resistant material. Both first vaporizer 106 and second vaporizer 113 may each operate at a temperature from 20° C. to 300° C. and at a pressure from 10 kPa to 3000 kPa. First vaporizer 106 produces the first vapor feed stream in line 107 by transferring the acetic acid from the liquid to gas phase below the boiling point of acetic acid in reactor 108 at the operating pressure of the reactor. In one embodiment, the acetic acid in the liquid state is maintained at a temperature below 160° C., e.g., below 150° C. or below 130° C. First vaporizer 106 may be operated at a temperature of at least 118° C.

Although two vaporizers are shown, it should be appreciated that additional vaporizers may be used for different liquid recycle streams and fresh feed streams. First vapor feed stream in line 107 is introduced at a location different than the second vapor feed stream in line 113. For example, first vapor feed stream in line 107 may be introduced at a location such that it pass through the entire catalyst beds within reactor 108 and second vapor feed stream in line 113 is introduced at a location such that is passes through a portion of the catalyst beds within reactor 108.

Reactor 108 contains the catalyst that is used in the hydrogenation of the carboxylic acid, preferably acetic acid. In one embodiment, one or more guard beds (not shown) may be used upstream of the reactor, optionally upstream of first vaporizer 106 and second vaporizer 113, to protect the catalyst from poisons or undesirable impurities contained in the feed or return/recycle streams. Such guard beds may be employed in the vapor or liquid streams. Suitable guard bed materials may include, for example, carbon, silica, alumina, ceramic, or resins. In one aspect, the guard bed media is functionalized, e.g., silver functionalized, to trap particular species such as sulfur or halogens. During the hydrogenation process, a crude ethanol product is withdrawn, preferably continuously, from reactor 108 via line 109.

The crude ethanol product in line 109 may be condensed and fed to a separator 110, which, in turn, provides a vapor stream 111 and a liquid stream 112. In some embodiments, separator 110 may comprise a flasher or a knockout pot. The separator 110 may operate at a temperature from 20° C. to 350° C., e.g., from 30° C. to 325° C. or from 60° C. to 250° C. The pressure of separator 110 may be from 100 kPa to 3000 kPa, e.g., from 125 kPa to 2500 kPa or from 150 kPa to 2200 kPa. Optionally, the crude ethanol product in line 109 may pass through one or more membranes to separate hydrogen and/or other non-condensable gases.

The vapor stream 111 exiting separator 110 may comprise hydrogen and hydrocarbons, and may be purged and/or returned to reaction zone 101. When returned to reaction zone 101, vapor stream 110 is combined with the hydrogen feed 104 and co-fed to vaporizer 106. In some embodiments, the returned vapor stream 111 may be compressed before being combined with hydrogen feed 104 or optional feed 114.

In FIG. 1, the liquid stream 112 from separator 110 is withdrawn and introduced in the lower part of first column 120, e.g., lower half or lower third. First column 120 is also referred to as an “acid separation column.” In one embodiment, the contents of liquid stream 112 are substantially similar to the crude ethanol product obtained from the reactor, except that the composition has been depleted of hydrogen, carbon dioxide, methane and/or ethane, which are removed by separator 110. Accordingly, liquid stream 112 may also be referred to as a crude ethanol product. Exemplary components of liquid stream 112 are provided in Table 2. It should be understood that liquid stream 112 may contain other components, not listed in Table 2.

TABLE 2 COLUMN FEED COMPOSITION (Liquid Stream 112) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Ethanol 5 to 70 10 to 70 15 to 65 Acetic Acid <90  0 to 50  0 to 35 Water 5 to 30  5 to 28 10 to 26 Ethyl Acetate <30 0.001 to 20    1 to 12 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetals 0.01 to 10   0.01 to 6   0.01 to 5   Acetone <5 0.0005 to 0.05  0.001 to 0.03  Other Esters <5 <0.005 <0.001 Other Ethers <5 <0.005 <0.001 Other Alcohols <5 <0.005 <0.001

The lower amounts indicated as less than (<) in the tables throughout the present specification may not be present and if present may be present in trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethyl propionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butyl acetate or mixtures thereof. The “other ethers” in Table 2 may include, but are not limited to, diethyl ether, methyl ethyl ether, isobutyl ethyl ether or mixtures thereof. The “other alcohols” in Table 2 may include, but are not limited to, methanol, isopropanol, n-propanol, n-butanol, 2-butanol or mixtures thereof. In one embodiment, the liquid stream 112 may comprise propanol, e.g., isopropanol and/or n-propanol, in an amount from 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03 wt. %. In should be understood that these other components may be carried through in any of the distillate or residue streams described herein and will not be further described herein, unless indicated otherwise.

Optionally, crude ethanol product in line 109 or in liquid stream 112 may be further fed to an esterification reactor, hydrogenolysis reactor, or combination thereof. An esterification reactor may be used to consume residual acetic acid present in the crude ethanol product to further reduce the amount of acetic acid that would otherwise need to be removed. Hydrogenolysis may be used to convert ethyl acetate in the crude ethanol product to ethanol.

In first column 120, unreacted acetic acid, a portion of the water, and other heavy components, if present, are removed from the composition in line 121 and are withdrawn, preferably continuously, as residue. Some or all of the residue may be returned and/or recycled back to reaction zone 101 via line 121. Recycling the acetic acid in line 121 to the vaporizer 106 may reduce the amount of heavies that need to be purged from vaporizer 106. Optionally, at least a portion of residue in line 121 may be purged from the system. Reducing the amount of heavies to be purged may improve efficiencies of the process while reducing byproducts.

First column 120 also forms an overhead distillate, which is withdrawn in line 122, and which may be condensed and refluxed, for example, at a ratio from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.

When column 120 is operated under standard atmospheric pressure, the temperature of the residue exiting in line 121 preferably is from 95° C. to 120° C., e.g., from 110° C. to 117° C. or from 111° C. to 115° C. The temperature of the distillate exiting in line 122 preferably is from 70° C. to 110° C., e.g., from 75° C. to 95° C. or from 80° C. to 90° C. Column 120 preferably operates at ambient pressure. In other embodiments, the pressure of first column 120 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary components of the distillate and residue compositions for first column 120 are provided in Table 3 below. It should also be understood that the distillate and residue may also contain other components, not listed, such as components in the feed. For convenience, the distillate and residue of the first column may also be referred to as the “first distillate” or “first residue.” The distillates or residues of the other columns may also be referred to with similar numeric modifiers (second, third, etc.) in order to distinguish them from one another, but such modifiers should not be construed as requiring any particular separation order.

TABLE 3 ACID COLUMN 120 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Distillate Ethanol 20 to 75 30 to 70 40 to 65 Water 10 to 40 15 to 35 20 to 35 Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate <60 5.0 to 40  10 to 30 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetals 0.01 to 10   0.05 to 6   0.1 to 5   Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue Acetic Acid  60 to 100 70 to 95 85 to 92 Water <30  1 to 20  1 to 15 Ethanol <1 <0.9 <0.07

As shown in Table 3, without being bound by theory, it has surprisingly and unexpectedly been discovered that when any amount of acetal is detected in the feed that is introduced to the acid separation column 120, the acetal appears to decompose in the column such that less or even no detectable amounts are present in the distillate and/or residue.

The distillate in line 122 preferably comprises ethanol, ethyl acetate, and water, along with other impurities, which may be difficult to separate due to the formation of binary and tertiary azeotropes. To further separate distillate, line 122 is introduced to the second column 123, also referred to as the “light ends column,” preferably in the middle part of column 123, e.g., middle half or middle third. Preferably the second column 123 is an extractive distillation column. In such embodiments, an extraction agent, such as water, may be added to second column 123. If the extraction agent comprises water, it may be obtained from an external source or from an internal return/recycle line from one or more of the other columns.

The molar ratio of the water in the extraction agent to the ethanol in the feed to the second column is preferably at least 0.5:1, e.g., at least 1:1 or at least 3:1. In terms of ranges, preferred molar ratios may range from 0.5:1 to 8:1, e.g., from 1:1 to 7:1 or from 2:1 to 6.5:1. Higher molar ratios may be used but with diminishing returns in terms of the additional ethyl acetate in the second distillate and decreased ethanol concentrations in the second column distillate.

In one embodiment, an additional extraction agent, such as water from an external source, dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethylene glycol-1,5-pentanediol; propylene glycol-tetraethylene glycol-polyethylene glycol; glycerine-propylene glycol-tetraethylene glycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane, N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine, diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, an alkylated thiopene, dodecane, tridecane, tetradecane and chlorinated paraffins, may be added to second column 123. Some suitable extraction agents include those described in U.S. Pat. Nos. 4,379,028, 4,569,726, 5,993,610 and 6,375,807, the entire contents and disclosure of which are hereby incorporated by reference.

In the embodiments of the present invention, without the use of an extractive agent, a larger portion of the ethanol would carry over into the second distillate in line 127. By using an extractive agent in second column 123, the separation of ethanol into the second residue in line 126 is facilitated thus increasing the yield of the overall ethanol product in the second residue in line 126.

Second column 123 may be a tray or packed column. In one embodiment, second column 123 is a tray column having from 5 to 70 trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Although the temperature and pressure of second column 123 may vary, when at atmospheric pressure the temperature of the second residue exiting in line 126 preferably is from 60° C. to 90° C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C. The temperature of the second distillate exiting in line 127 from second column 123 preferably is from 50° C. to 90° C., e.g., from 60° C. to 80° C. or from 60° C. to 70° C. Column 123 may operate at atmospheric pressure. In other embodiments, the pressure of second column 123 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary components for the distillate and residue compositions for second column 123 are provided in Table 4 below. It should be understood that the distillate and residue may also contain other components, not listed, such as components in the feed.

TABLE 4 SECOND COLUMN 123 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Distillate Ethyl Acetate 10 to 99 25 to 95 50 to 93 Acetaldehyde <25 0.5 to 15  1 to 8 Water <25 0.5 to 20   4 to 16 Ethanol <30 0.001 to 15   0.01 to 5   Acetal 0.01 to 20    1 to 20  5 to 20 Residue Water 30 to 90 40 to 85 50 to 85 Ethanol 10 to 75 15 to 60 20 to 50 Ethyl Acetate <3 0.001 to 2    0.001 to 0.5  Acetic Acid <0.5 0.001 to 0.3  0.001 to 0.2 

In preferred embodiments, the use of an extraction agent, such as the recycling of the third residue, as discussed in detail below, promotes the separation of ethyl acetate from the residue of the second column 123. For example, the weight ratio of ethyl acetate in the second residue to second distillate preferably is less than 0.4:1, e.g., less than 0.2:1 or less than 0.1:1. In embodiments that use an extractive distillation column with water as an extraction agent as the second column 123, the weight ratio of ethyl acetate in the second residue to ethyl acetate in the second distillate approaches zero. Second residue may comprise, for example, from 30% to 99.5% of the water and from 85 to 100% of the acetic acid from line 122. The second distillate in line 127 comprises ethyl acetate and additionally comprises water, ethanol, and/or acetaldehyde. Second distillate 127 is preferably substantially free of acetic acid. At least a portion of second distillate 127 is combined with line 132 (discussed below) and fed to vaporizer 113.

The weight ratio of ethanol in the second residue to second distillate preferably is at least 3:1, e.g., at least 6:1, at least 8:1, at least 10:1 or at least 15:1. All or a portion of the third residue is recycled to the second column. In one embodiment, all of the third residue may be recycled until process 100 reaches a steady state and then a portion of the third residue is recycled with the remaining portion being purged from the system 100. The composition of the second residue will tend to have lower amounts of ethanol than when the third residue is not recycled. As the third residue is recycled, the composition of the second residue, as provided in Table 4, comprises less than 30 wt. % of ethanol, e.g., less than 20 wt. % or less than 15 wt. %. The majority of the second residue preferably comprises water. Notwithstanding this effect, the extractive distillation step advantageously also reduces the amount of ethyl acetate that is sent to the third column, which is highly beneficial in ultimately forming a highly pure ethanol product.

As shown, the second residue from second column 123, which comprises ethanol and water, is fed via line 126 to third column 128, also referred to as the “product column.” More preferably, the second residue in line 126 is introduced in the lower part of third column 128, e.g., lower half or lower third. Third column 128 recovers ethanol, which preferably is substantially pure with respect to organic impurities and other than the azeotropic water content, as the distillate in line 129. The distillate of third column 128 preferably is refluxed as shown in FIG. 1, for example, at a reflux ratio from 1:10 to 10:1, e.g., from 1:3 to 3:1 or from 1:2 to 2:1. The third residue in line 130, which comprises primarily water, preferably is returned to the second column 123 as an extraction agent as described above. In one embodiment (not shown), a first portion of the third residue in line 130 is recycled to the second column and a second portion is purged and removed from the system. In one embodiment, once the process reaches steady state, the second portion of water to be purged is substantially similar to the amount water formed in the hydrogenation of acetic acid. In one embodiment, a portion of the third residue may be used to hydrolyze any other stream, such as one or more streams comprising ethyl acetate.

Third column 128 is preferably a tray column as described above and operates at atmospheric pressure or optionally at pressures above or below atmospheric pressure. The temperature of the third distillate exiting in line 129 preferably is from 50° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature of the third residue in line 124 preferably is from 15° C. to 100° C., e.g., from 30° C. to 90° C. or from 50° C. to 80° C. Exemplary components of the distillate and residue compositions for third column 128 are provided in Table 5 below. It should be understood that the distillate and residue may also contain other components, not listed, such as components in the feed.

TABLE 5 THIRD COLUMN 128 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Distillate Ethanol 75 to 96  80 to 96  85 to 96 Water <12  1 to 9  3 to 8 Acetic Acid <12 0.0001 to 0.1  0.005 to 0.05 Ethyl Acetate <12 0.0001 to 0.05  0.005 to 0.025 Acetaldehyde <12 0.0001 to 0.1  0.005 to 0.05 Acetal <12 0.0001 to 0.05 0.005 to 0.01 Residue Water  75 to 100   80 to 100  90 to 100 Ethanol <0.8 0.001 to 0.5 0.005 to 0.05 Ethyl Acetate <1 0.001 to 0.5 0.005 to 0.2  Acetic Acid <2 0.001 to 0.5 0.005 to 0.2 

Any of the compounds that are carried through the distillation process from the feed or crude reaction product generally remain in the third distillate in amounts of less 0.1 wt. %, based on the total weight of the third distillate composition, e.g., less than 0.05 wt. % or less than 0.02 wt. %. In one embodiment, one or more side streams may remove impurities from any of the columns in the system 100. Preferably at least one side stream is used to remove impurities from the third column 128. The impurities may be purged and/or retained within the system 100.

The third distillate in line 129 may be further purified to form an anhydrous ethanol product stream, i.e., “finished anhydrous ethanol,” using one or more additional separation systems, such as, for example, distillation columns, adsorption units, membranes, or molecular sieves. Suitable adsorption units include pressure swing adsorption units and thermal swing adsorption unit.

Returning to second column 123, the second distillate preferably is refluxed as shown in FIG. 1, optionally at a reflux ratio of 1:10 to 10:1, e.g., from 1:5 to 5:1 or from 1:3 to 3:1. As explained above, at least a portion of second distillate in line 127 may be purged or a portion may be recycled to the reaction zone as the liquid recycle stream and fed to second vaporizer 113. In one embodiment, at least a portion of second distillate in line 127 is further processed in fourth column 131, also referred to as the “acetaldehyde removal column.” In fourth column 131, the second distillate is separated into a fourth distillate, which comprises acetaldehyde, in line 132 and a fourth residue, which comprises ethyl acetate, in line 133. The fourth distillate preferably is refluxed at a reflux ratio from 1:20 to 20:1, e.g., from 1:15 to 15:1 or from 1:10 to 10:1, and at least a portion of the fourth distillate is returned to vaporizer 113. Additionally, at least a portion of fourth distillate in line 132 may be purged. Without being bound by theory, since acetaldehyde may be reacted, e.g., by hydrogenation, to form ethanol, the recycling of a stream that contains acetaldehyde to the reaction zone increases the yield of ethanol and decreases byproduct and waste generation. In another embodiment, the acetaldehyde may be collected and utilized, with or without further purification, to make useful products including but not limited to n-butanol, 1,3-butanediol, and/or crotonaldehyde and derivatives.

The fourth residue of fourth column 131 may be purged via line 133. The fourth residue primarily comprises ethyl acetate and ethanol, which may be suitable for use as a solvent mixture or in the production of esters. In one preferred embodiment, the acetaldehyde is removed from the second distillate in optional fourth column 131 such that no detectable amount of acetaldehyde is present in the residue of column 131.

Fourth column 131 is a tray column as described above and may operate above atmospheric pressure. In one embodiment, the pressure is from 120 kPa to 5,000 kPa, e.g., from 200 kPa to 4,500 kPa, or from 400 kPa to 3,000 kPa. In a preferred embodiment the fourth column 131 may operate at a pressure that is higher than the pressure of the other columns.

The temperature of the fourth distillate exiting in line 132 preferably is from 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature of the residue in line 133 preferably is from 70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 110° C. Exemplary components of the distillate and residue compositions for optional fourth column 131 are provided in Table 6 below. It should be understood that the distillate and residue may also contain other components, not listed, such as components in the feed.

TABLE 6 FOURTH COLUMN 131 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Distillate Acetaldehyde 2 to 80    2 to 50   5 to 40 Ethyl Acetate <90   30 to 80   40 to 75 Ethanol <30 0.001 to 25 0.01 to 20 Water <25 0.001 to 20 0.01 to 15 Residue Ethyl Acetate 40 to 100    50 to 100   60 to 100 Ethanol <40 0.001 to 30 0.01 to 15 Water <25 0.001 to 20   2 to 15 Acetaldehyde <1  0.001 to 0.5 Not detectable Acetal <3 0.0001 to 2   0.001 to 0.01

In one embodiment, a portion of the third residue in line 130 is recycled to second column 123. In one embodiment, recycling the third residue further reduces the aldehyde components in the second residue and concentrates these aldehyde components in second distillate in line 127 and thereby sent to optional fourth column 131, wherein the aldehydes may be more easily separated. The third distillate in line 129 may have lower concentrations of aldehydes and esters due to the recycling of third residue in line 124.

FIG. 2 illustrates another exemplary separation system. The reaction zone 101 of FIG. 2 is similar to FIG. 1 and produces a liquid stream 112, e.g., crude ethanol product, for further separation. In one preferred embodiment, the reaction zone 101 of FIG. 2 operates at above 80% acetic acid conversion, e.g., above 90% conversion or above 99% conversion. Thus, the acetic acid concentration in the liquid stream 112 may be low.

Liquid stream 112 is introduced in the middle or lower portion of a first column 150, also referred to as acid-water column. For purposes of convenience, the columns in each exemplary separation process, may be referred as the first, second, third, etc., columns, but it is understood that first column 150 in FIG. 2 operates differently than the first column 120 of FIG. 1. In one embodiment, no entrainers are added to first column 150. In FIG. 2, first column 150, water and unreacted acetic acid, along with any other heavy components, if present, are removed from liquid stream 112 and are withdrawn, preferably continuously, as a first residue in line 151. Preferably, a substantial portion of the water in the crude ethanol product that is fed to first column 150 may be removed in the first residue, for example, up to about 75% or to about 90% of the water from the crude ethanol product. First column 150 also forms a first distillate, which is withdrawn in line 152.

When column 150 is operated under about 170 kPa, the temperature of the residue exiting in line 151 preferably is from 90° C. to 130° C., e.g., from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of the distillate exiting in line 152 preferably is from 60° C. to 90° C., e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In some embodiments, the pressure of first column 150 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 152 comprises water, in addition to ethanol and other organics. In terms of ranges, the concentration of water in the first distillate in line 152 preferably is from 4 wt. % to 38 wt. %, e.g., from 7 wt. % to 32 wt. %, or from 7 to 25 wt. %. A portion of first distillate in line 153 may be condensed and refluxed, for example, at a ratio from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1. It is understood that reflux ratios may vary with the number of stages, feed locations, column efficiency and/or feed composition. Operating with a reflux ratio of greater than 3:1 may be less preferred because more energy may be required to operate the first column 150. The condensed portion of the first distillate may also be fed to a second column 154.

The remaining portion of the first distillate in 152 is fed to a water separation unit 156. Water separation unit 156 may be an adsorption unit, membrane, molecular sieves, extractive column distillation, or a combination thereof. A membrane or an array of membranes may also be employed to separate water from the distillate. The membrane or array of membranes may be selected from any suitable membrane that is capable of removing a permeate water stream from a stream that also comprises ethanol and ethyl acetate.

In a preferred embodiment, water separator 156 is a pressure swing adsorption (PSA) unit. The PSA unit is optionally operated at a temperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and a pressure from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSA unit may comprise two to five beds. Water separator 156 may remove water in an amount necessary for the ethanol product, which may vary. For hydrous ethanol applications, water separator 156 may remove water in an amount greater than 10% of the water from the portion of first distillate in line 152, e.g., greater than 20% or greater than 35%. For anhydrous ethanol applications, water separator 156 may remove at least 95% of the water from the portion of first distillate in line 152, and more preferably from 95% to 99.99% of the water from the first distillate, in a water stream 157. All or a portion of water stream 157 may be returned to column 150 in line 158, where the water preferably is ultimately recovered from column 150 in the first residue in line 151. Additionally or alternatively, all or a portion of water stream 157 may be purged via line 159. The remaining portion of first distillate exits the water separator 156 as ethanol mixture stream 160. Ethanol mixture stream 160 may have a low concentration of water of less than 10 wt. %, e.g., less than 6 wt. % or less than 2 wt. %. Exemplary components of ethanol mixture stream 160 and first residue in line 151 are provided in Table 7 below. It should also be understood that these streams may also contain other components, not listed, such as components derived from the feed.

TABLE 7 FIRST COLUMN 150 WITH PSA (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Ethanol Mixture Stream Ethanol 20 to 95 30 to 95 40 to 95 Water <10 0.01 to 6   0.1 to 2   Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate <60  1 to 55  5 to 55 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetal <0.1 <0.1 <0.05 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue Acetic Acid <90  1 to 50  2 to 35 Water  30 to 100 45 to 95 60 to 90 Ethanol <1 <0.9 <0.3 

Preferably, ethanol mixture stream 160 is not returned or refluxed to first column 150. The condensed portion of the first distillate in line 153 may be combined with ethanol mixture stream 160 to control the water concentration fed to the second column 154. For example, in some embodiments the first distillate may be split into equal portions, while in other embodiments, all of the first distillate may be condensed or all of the first distillate may be processed in the water separation unit. In FIG. 2, the condensed portion in line 153 and ethanol mixture stream 160 are co-fed to second column 154. In other embodiments, the condensed portion in line 153 and ethanol mixture stream 160 may be separately fed to second column 154. The combined distillate and ethanol mixture has a total water concentration of greater than 0.5 wt. %, e.g., greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, the total water concentration of the combined distillate and ethanol mixture may be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10 wt. %.

The second column 154 in FIG. 2, also referred to as the “light ends column,” removes ethyl acetate and acetaldehyde from the first distillate in line 153 and/or ethanol mixture stream 160. Ethyl acetate and acetaldehyde are removed as a second distillate in line 161 and ethanol is removed as the second residue in line 162. Second column 108 may be a tray column or packed column. In one embodiment, second column 154 is a tray column having from 5 to 70 trays, e.g., from 15 to 50 trays or from 20 to 45 trays.

Second column 154 operates at a pressure ranging from 0.1 kPa to 510 kPa, e.g., from 10 kPa to 450 kPa or from 50 kPa to 350 kPa. Although the temperature of second column 154 may vary, when at about 20 kPa to 70 kPa, the temperature of the second residue exiting in line 162 preferably is from 30° C. to 75° C., e.g., from 35° C. to 70° C. or from 40° C. to 65° C. The temperature of the second distillate exiting in line 161 preferably is from 20° C. to 55° C., e.g., from 25° C. to 50° C. or from 30° C. to 45° C.

The total concentration of water fed to second column 154 preferably is less than 10 wt. %, as discussed above. When first distillate in line 153 and/or ethanol mixture stream comprises minor amounts of water, e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may be fed to the second column 154 as an extractive agent in the upper portion of the column. A sufficient amount of water is preferably added via the extractive agent such that the total concentration of water fed to second column 154 is from 1 to 10 wt. % water, e.g., from 2 to 6 wt. %, based on the total weight of all components fed to second column 154. If the extractive agent comprises water, the water may be obtained from an external source or from an internal return/recycle line from one or more of the other columns or water separators.

Suitable extractive agents may also include, for example, dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethylene glycol-1,5-pentanediol; propylene glycol-tetraethylene glycol-polyethylene glycol; glycerine-propylene glycol-tetraethylene glycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane, N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine, diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, an alkylated thiopene, dodecane, tridecane, tetradecane, chlorinated paraffins, or a combination thereof. When extractive agents are used, a suitable recovery system, such as a further distillation column, may be used to recycle the extractive agent.

Exemplary components for the second distillate and second residue compositions for the second column 154 are provided in Table 8, below. It should be understood that the distillate and residue may also contain other components, not listed in Table 8.

TABLE 8 SECOND COLUMN 154 (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Second Distillate Ethyl Acetate 5 to 90 10 to 80 15 to 75 Acetaldehyde <60  1 to 40  1 to 35 Ethanol <45 0.001 to 40   0.01 to 35   Water <20 0.01 to 10   0.1 to 5   Second Residue Ethanol  80 to 99.5 85 to 97 60 to 95 Water <20 0.001 to 15   0.01 to 10   Ethyl Acetate <1 0.001 to 2    0.001 to 0.5  Acetic Acid <0.5 <0.01 0.001 to 0.01  Acetal <0.05 <0.03 <0.01

The second residue in FIG. 2 comprises one or more impurities selected from the group consisting of ethyl acetate, acetic acid, and acetaldehyde. The second residue may comprise at least 100 wppm of these impurities, e.g., at least 250 wppm or at least 500 wppm. In some embodiments, the second residue may contain substantially no ethyl acetate or acetaldehyde.

The second distillate in line 161, which comprises ethyl acetate and/or acetaldehyde, preferably is refluxed as shown in FIG. 2, for example, at a reflux ratio from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3 to 3:1. In one aspect, second distillate 161 or a portion thereof is returned to second vaporizer 113. Additionally, at least a portion of second distillate 161 may be purged.

FIG. 3 illustrates another exemplary separation system. The reaction zone 101 of FIG. 3 is similar to FIG. 1 and produces a liquid stream 112, e.g., crude ethanol product, for further separation. In one preferred embodiment, the reaction zone 101 of FIG. 3 operates at above 80% acetic acid conversion, e.g., above 90% conversion or above 99% conversion. Thus, the acetic acid concentration in the liquid stream 112 may be low.

In the exemplary embodiment shown in FIG. 3, liquid stream 112 is introduced in the upper part of first column 170, e.g., upper half or upper third. In addition to liquid stream 112, an optional extractive agent (not shown) and an optional ethyl acetate recycle stream in line 179 may also be fed to first column 170. The optional extractive agent may comprise water that is introduced above the feed location of the liquid stream 112. In some embodiment, the optional extractive agent may be a dilute acid stream comprising up to 20 wt. % acetic acid. Also, the optional ethyl acetate recycle stream may have a relatively high ethanol concentration, e.g. from 70 to 90 wt. %, and may be fed above or near the feed point of the liquid stream 112.

In one embodiment, first column 170 is a tray column having from 5 to 90 theoretical trays, e.g. from 10 to 60 theoretical trays or from 15 to 50 theoretical trays. The number of actual trays for each column may vary depending on the tray efficiency, which is typically from 0.5 to 0.7 depending on the type of tray. The trays may be sieve trays, fixed valve trays, movable valve trays, or any other suitable design known in the art. In other embodiments, a packed column having structured packing or random packing may be employed.

When first column 170 is operated under 50 kPa, the temperature of the residue exiting in line 171 preferably is from 20° C. to 100° C., e.g., from 30° C. to 90° C. or from 40° C. to 80° C. The base of column 170 may be maintained at a relatively low temperature by withdrawing a residue stream comprising ethanol, ethyl acetate, water, and acetic acid, thereby providing an energy efficiency advantage. The temperature of the distillate exiting in line 172 preferably at 50 kPa is from 10° C. to 80° C., e.g., from 20° C. to 70° C. or from 30° C. to 60° C. The pressure of first column 170 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In some embodiments, first column 170 may operate under a vacuum of less than 70 kPa, e.g., less than 50 kPa, or less than 20 kPa. Operating under a vacuum may decrease the reboiler duty and reflux ratio of first column 170. However, a decrease in operating pressure for first column 170 does not substantially affect column diameter.

In first column 170, a weight majority of the ethanol, water, acetic acid, are removed from an organic feed, which comprises liquid stream 112 and the optional ethyl acetate recycle stream in line 179, and are withdrawn, preferably continuously, as residue in line 171. This includes any water added as the optional extractive agent. Concentrating the ethanol in the residue reduces the amount of ethanol that is recycled to reactor 108 and in turn reduces the size of reactor 108. Preferably less than 10% of the ethanol from the organic feed, e.g., less than 5% or less than 1% of the ethanol, is returned to reactor 108 from first column 170. In addition, concentrating the ethanol also will concentrate the water and/or acetic acid in the residue. In one embodiment, at least 90% of the ethanol from the organic feed is withdrawn in the residue, and more preferably at least 95%. In addition, ethyl acetate may also be present in the first residue in line 171. The reboiler duty may decrease with an ethyl acetate concentration increase in the first residue in line 171.

First column 170 also forms a distillate, which is withdrawn in line 172, and which may be condensed and refluxed, for example, at a ratio from 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 5:1 to 1:5. Higher mass flow ratios of water to organic feed may allow first column 170 to operate with a reduced reflux ratio.

First distillate in line 172 preferably comprises a weight majority of the acetaldehyde and ethyl acetate from liquid stream 112, as well as from the optional ethyl acetate recycle stream in line 179. In one embodiment, the first distillate in line 172 comprises a concentration of ethyl acetate that is less than the ethyl acetate concentration for the azeotrope of ethyl acetate and water, and more preferably less than 75 wt. %.

In some embodiments, first distillate in stream 172 also comprises ethanol. Returning the first distillate comprising ethanol to the reactor may require an increase in reactor capacity to maintain the same level of ethanol efficiency. In one embodiment, it is preferred to return to the reactor less than 10% of the ethanol from the crude ethanol stream, e.g., less than 5% or less than 1%. In terms of ranges, the amount of returned ethanol is from 0.01 to 10% of the ethanol in the crude ethanol stream, e.g. from 0.1 to 5% or from 0.2 to 1%. In one embodiment, to reduce the amount of ethanol returned, the ethanol may be recovered from the first distillate in line 172 using an optional extractor or extractive distillation column.

Exemplary components of the distillate and residue compositions for first column 170 are provided in Table 9 below. It should also be understood that the distillate and residue may also contain other components, not listed in Table 9. For convenience, the distillate and residue of the first column may also be referred to as the “first distillate” or “first residue.” The distillates or residues of the other columns may also be referred to with similar numeric modifiers (second, third, etc.) in order to distinguish them from one another, but such modifiers should not be construed as requiring any particular separation order.

TABLE 9 FIRST COLUMN 170 (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Distillate Ethyl Acetate 10 to 85 15 to 80 20 to 75 Acetaldehyde 0.1 to 70  0.2 to 65  0.5 to 65  Acetal <0.1 <0.1 <0.05 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Ethanol  3 to 55  4 to 50  5 to 45 Water 0.1 to 20   1 to 15  2 to 10 Acetic Acid <2 <0.1 <0.05 Residue Acetic Acid 0.1 to 50  0.5 to 40   1 to 30 Water  5 to 40  5 to 35 10 to 25 Ethanol 10 to 75 15 to 70 20 to 65 Ethyl Acetate 0.005 to 30   0.03 to 25   0.08 to 1  

In one embodiment of the present invention, first column 170 may be operated at a temperature where most of the water, ethanol, and acetic acid are removed into the residue stream and only a small amount of ethanol and water is collected in the distillate stream due to the formation of binary and tertiary azeotropes. The weight ratio of water in the residue in line 171 to water in the distillate in line 172 may be greater than 1:1, e.g., greater than 2:1. There may be more water in residue in line 171 when an optional extractive agent is used. The weight ratio of ethanol in the residue to ethanol in the distillate may be greater than 1:1, e.g., greater than 2:1.

The amount of acetic acid in the first residue may vary depending primarily on the conversion in reactor 108. In one embodiment, when the conversion is high, e.g., greater than 90%, the amount of acetic acid in the first residue may be less than 10 wt. %, e.g., less than 5 wt. % or less than 2 wt. %. In other embodiments, when the conversion is lower, e.g., less than 90%, the amount of acetic acid in the first residue may be greater than 10 wt. %.

The distillate preferably is substantially free of acetic acid, e.g., comprising less than 1000 ppm, less than 500 ppm or less than 100 ppm acetic acid. The distillate may be purged from the system or recycled in whole or part to reactor 108. In some embodiments, the distillate may be further separated, e.g., in a distillation column (not shown), into an acetaldehyde stream and an ethyl acetate stream. Either of these streams may be returned to reactor 108 or separated from system 100 as additional products. The ethyl acetate stream may also be hydrolyzed or reduced with hydrogen, via hydrogenolysis, to produce ethanol. When additional ethanol is produced, it is preferred that the additional ethanol is recovered and not directed to reactor 108.

Some species, such as acetals, may decompose in first column 170 such that very low amounts, or even no detectable amounts, of acetals remain in the distillate or residue.

To recover ethanol, first residue in line 171 may be further separated depending on the concentration of acetic acid and/or ethyl acetate. In FIG. 3, residue in line 171 is further separated in a second column 173, also referred to as an “acid column.” Second column 173 yields a second residue in line 174 comprising acetic acid and water, and a second distillate in line 175 comprising ethanol and ethyl acetate. In one embodiment, a weight majority of the water and/or acetic acid fed to second column 173 is removed in the second residue in line 174, e.g., at least 60% of the water and/or acetic acid is removed in the second residue in line 174 or more preferably at least 80% of the water and/or acetic acid. An acid column may be desirable, for example, when the acetic acid concentration in the first residue is greater 50 wppm, e.g., greater than 0.1 wt. %, greater than 1 wt. %, e.g., greater than 5 wt. %.

In one embodiment, a portion of the first residue in line 171 may be preheated prior to being introduced into second column 173, as shown in FIG. 3. After preheating first residue in ine 171 may be converted into a partial vapor feed having less than 30 mol. % of the contents in the vapor phase, e.g., less than 25 mol. % or less than 20 mol. %. In terms of ranges, from 1 to 30 mol. % is in the vapor phase, e.g., from 5 to 20 mol. %. Greater vapor phase contents result in increased energy consumption and a significant increase in the size of second column 173.

Second column 173 operates in a manner to concentrate the ethanol from first residue so that a majority of the ethanol is carried overhead. Thus, the residue of second column 173 may have a low ethanol concentration of less than 5 wt. %, e.g. less than 1 wt. % or less than 0.5 wt. %. Lower ethanol concentrations may be achieved without significant increases in reboiler duty or column size. Thus, in some embodiments, it is efficient to reduce the ethanol concentration in the residue to less than 50 wppm, or more preferably less than 25 wppm. As described herein, the residue of second column 173 may be treated and lower concentrations of ethanol allow the residue to be treated without generating further impurities.

In FIG. 3, the first residue in line 171 is introduced to second column 173 preferably in the top part of column 173, e.g., top half or top third. Feeding first residue in line 171 in a lower portion of second column 173 may unnecessarily increase the energy requirements. Acid column 173 may be a tray column or packed column. In FIG. 3, second column 173 may be a tray column having from 10 to 110 theoretical trays, e.g. from 15 to 95 theoretical trays or from 20 to 75 theoretical trays. Additional trays may be used if necessary to further reduce the ethanol concentration in the residue. In one embodiment, the reboiler duty and column size may be reduced by increasing the number of trays.

Although the temperature and pressure of second column 173 may vary, when at atmospheric pressure the temperature of the second residue in line 174 preferably is from 95° C. to 160° C., e.g., from 100° C. to 150° C. or from 110° C. to 145° C. In one embodiment, first residue in line 171 is preheated to a temperature that is within 20° C. of the temperature of second residue in line 174, e.g., within 15° C. or within 10° C. The temperature of the second distillate exiting in line 175 from second column 173 preferably is from 50° C. to 120° C., e.g., from 75° C. to 118° C. or from 80° C. to 115° C. The temperature gradient may be sharper in the base of second column 173.

The pressure of second column 173 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In one embodiment, second column 173 operates above atmospheric pressure, e.g., above 170 kPa or above 375 kPa. Second column 173 may be constructed of a material such as 316 L SS, Allot 2205 or Hastelloy C, depending on the operating pressure. The reboiler duty and column size for second column 173 remain relatively constant until the ethanol concentration in the second distillate in line 175 is greater than 90 wt. %.

Second column 173 also forms an overhead, which is withdrawn, and which may be condensed and refluxed, for example, at a ratio from 12:1 to 1:12, e.g., from 10:1 to 1:10 or from 8:1 to 1:8. The overhead preferably comprises 85 to 92 wt. % ethanol, e.g., about 87 to 90 wt. % ethanol, with the remaining balance being water and ethyl acetate. In one embodiment, water may be removed prior to recovering the ethanol product as described above in FIG. 2. In one embodiment, the overhead, prior to water removal, may comprise less than 15 wt. % water, e.g., less than 10 wt. % water or less than 8 wt. % water. Overhead vapor may be fed to water separator, which may be an adsorption unit, membrane, molecular sieves, extractive column distillation, or a combination thereof.

Exemplary components for the distillate and residue compositions for second column 173 are provided in Table 10 below. It should be understood that the distillate and residue may also contain other components, not listed in Table 10. For example, in optional embodiments, when ethyl acetate is in the feed to reactor 108, second residue in line 174 exemplified in Table 10 may also comprise high boiling point components.

TABLE 10 SECOND COLUMN 173 (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Second Distillate Ethanol 80 to 96   85 to 92 87 to 90 Ethyl Acetate <30 0.001 to 15 0.005 to 4    Acetaldehyde <20 0.001 to 15 0.005 to 4    Water <20 0.001 to 10 0.01 to 8   Acetal <2 0.001 to 1  0.005 to 0.5  Second Residue Acetic Acid 0.1 to 55   0.2 to 40 0.5 to 35  Water 45 to 99.9     55 to 99.8   65 to 99.5 Ethyl Acetate <0.1  0.0001 to 0.05 0.0001 to 0.01  Ethanol <5 0.002 to 1  0.005 to 0.5 

The weight ratio of ethanol in second distillate in line 175 to ethanol in the second residue in line 174 preferably is at least 35:1. Preferably, second distillate in line 175 is substantially free of acetic acid and may contain, if any, trace amounts of acetic acid.

In one embodiment, ethyl acetate fed to second column 173 may concentrate in the second distillate in line 175. Thus, preferably no ethyl acetate is withdrawn in the second residue in line 174. Advantageously this allows most of the ethyl acetate to be subsequently recovered without having to further process the second residue in line 174.

In one embodiment, as shown in FIG. 3, due to the presence of ethyl acetate in second distillate in line 175, an additional third column 176 may be used. Third column 176, referred to as a “product” column, is used for removing ethyl acetate from second distillate in line 175 and producing an ethanol product in the third residue in line 177. Product column 176 may be a tray column or packed column. In FIG. 3, third column 176 may be a tray column having from 5 to 90 theoretical trays, e.g. from 10 to 60 theoretical trays or from 15 to 50 theoretical trays.

The feed location of second distillate in line 175 may vary depending on ethyl acetate concentration and it is preferred to feed second distillate in line 175 to the upper portion of third column 176. Higher concentrations of ethyl acetate may be fed at a higher location in third column 176. The feed location should avoid the very top trays, near the reflux, to avoid excess reboiler duty requirements for the column and an increase in column size. For example, in a column having 45 actual trays, the feed location should between 10 to 15 trays from the top. Feeding at a point above this may increase the reboiler duty and size of third column 176.

Second distillate in line 175 may be fed to third column 176 at a temperature of up to 70° C., e.g., up to 50° C., or up to 40° C. In some embodiments it is not necessary to further preheat second distillate in line 175.

Ethyl acetate may be concentrated in the third distillate in line 178. Due to the relatively lower amounts of ethyl acetate fed to third column 176, third distillate in line 178 also comprises substantial amounts of ethanol. To recover the ethanol, third distillate in line 178 may be fed to first column 170 as an optional ethyl acetate recycle stream 179. Depending on the ethyl acetate concentration of optional ethyl acetate recycle stream 179 this stream may be introduced above or near the feed point of the liquid stream 112. Depending on the targeted ethyl acetate concentration in the distillate of first column 172 the feed point of optional ethyl acetate recycle stream 179 will vary. Liquid stream 112 and optional ethyl acetate recycle stream 179 collectively comprise the organic feed to first column 170. In one embodiment, organic feed comprises from 1 to 25% of optional ethyl acetate recycle stream 179, e.g., from 3% to 20% or from 5% to 15%. This amount may vary depending on the production of reactor 108 and amount of ethyl acetate to be recycled.

Because optional ethyl acetate recycle stream 179 increases the demands on the first and second columns, it is preferred that the ethanol concentration in third distillate in line 179 be from 70 to 90 wt. %, e.g., from 72 to 88 wt. %, or from 75 to 85 wt. %. In other embodiments, a portion of third distillate in line 178 may be purged from the system as additional products, such as an ethyl acetate solvent. In addition, ethanol may be recovered from a portion of the third distillate in line 178 using an extractant, such as benzene, propylene glycol, and cyclohexane, so that the raffinate comprises less ethanol to recycle.

In an optional embodiment, the third residue may be further processed to recover ethanol with a desired amount of water, for example, using a further distillation column, adsorption unit, membrane or combination thereof, may be used to further remove water from third residue in line 177 as necessary.

Third column 176 is preferably a tray column as described above and preferably operates at atmospheric pressure. The temperature of the third residue in line 177 exiting from third column 176 preferably is from 65° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to 80° C. The temperature of the third distillate in line 178 exiting from third column 176 preferably is from 30° C. to 70° C., e.g., from 40° C. to 65° C. or from 50° C. to 65° C.

The pressure of third column 176 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In some embodiments, third column 176 may operate under a vacuum of less than 70 kPa, e.g., less than 50 kPa, or less than 20 kPa. Decreases in operating pressure substantially decreases column diameter and reboiler duty for third column 176.

Exemplary components for ethanol mixture stream and residue compositions for third column 176 are provided in Table 11 below. It should be understood that the distillate and residue may also contain other components, not listed in Table 11.

TABLE 11 PRODUCT COLUMN (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Third Distillate Ethanol 70 to 99 72 to 95 75 to 90 Ethyl Acetate  1 to 30  1 to 25  1 to 15 Acetaldehyde <15 0.001 to 10   0.1 to 5   Water <10 0.001 to 2    0.01 to 1   Acetal <2 0.001 to 1    0.01 to 0.5  Third Residue Ethanol   80 to 99.5 85 to 97 90 to 95 Water <3 0.001 to 2    0.01 to 1   Ethyl Acetate <1.5 0.0001 to 1    0.001 to 0.5  Acetic Acid <0.5 <0.01 0.0001 to 0.01 

Some of the residues withdrawn from the separation zone 102 comprise acetic acid and water. Depending on the amount of water and acetic acid contained in the residue of first column, e.g., 120 in FIG. 1, 150 in FIG. 2, or residue of second column 173 in FIG. 3, the residue may be treated in one or more of the following processes. The following are exemplary processes for further treating the residue and it should be understood that any of the following may be used regardless of acetic acid concentration. When the residue comprises a majority of acetic acid, e.g., greater than 70 wt. %, the residue may be recycled to the reactor without any separation of the water. In one embodiment, the residue may be separated into an acetic acid stream and a water stream when the residue comprises a majority of acetic acid, e.g., greater than 50 wt. %. Acetic acid may also be recovered in some embodiments from the residue having a lower acetic acid concentration. The residue may be separated into the acetic acid and water streams by a distillation column or one or more membranes. If a membrane or an array of membranes is employed to separate the acetic acid from the water, the membrane or array of membranes may be selected from any suitable acid resistant membrane that is capable of removing a permeate water stream. The resulting acetic acid stream optionally is returned to the reactor 108. The resulting water stream may be used as an extractive agent or to hydrolyze an ester-containing stream in a hydrolysis unit.

In other embodiments, for example, where the residue comprises less than 50 wt. % acetic acid, possible options include one or more of: (i) returning a portion of the residue to reactor 108, (ii) neutralizing the acetic acid, (iii) reacting the acetic acid with an alcohol, or (iv) disposing of the residue in a waste water treatment facility. It also may be possible to separate a residue comprising less than 50 wt. % acetic acid using a weak acid recovery distillation column to which a solvent (optionally acting as an azeotroping agent) may be added. Exemplary solvents that may be suitable for this purpose include ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, vinyl acetate, diisopropyl ether, carbon disulfide, tetrahydrofuran, isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the acetic acid, it is preferred that the residue comprises less than 10 wt. % acetic acid. Acetic acid may be neutralized with any suitable alkali or alkaline earth metal base, such as sodium hydroxide or potassium hydroxide. When reacting acetic acid with an alcohol, it is preferred that the residue comprises less than 50 wt. % acetic acid. The alcohol may be any suitable alcohol, such as methanol, ethanol, propanol, butanol, or mixtures thereof. The reaction forms an ester that may be integrated with other systems, such as carbonylation production or an ester production process. Preferably, the alcohol comprises ethanol and the resulting ester comprises ethyl acetate. Optionally, the resulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the residue comprises very minor amounts of acetic acid, e.g., less than 5 wt. %, the residue may be disposed of to a waste water treatment facility without further processing. The organic content, e.g., acetic acid content, of the residue beneficially may be suitable to feed microorganisms used in a waste water treatment facility.

The columns shown in FIGS. 1 to 3 may comprise any distillation column capable of performing the desired separation and/or purification. Each column preferably comprises a tray column having from 1 to 150 trays, e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays. The trays may be sieve trays, fixed valve trays, movable valve trays, or any other suitable design known in the art. In other embodiments, a packed column may be used. For packed columns, structured packing or random packing may be employed. The trays or packing may be arranged in one continuous column or they may be arranged in one or more columns, preferably two or more columns such that the vapor from the first section enters the second section while the liquid from the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may be employed with each of the distillation columns may be of any conventional design and are simplified in the figures. Heat may be supplied to the base of each column or to a circulating bottom stream through a heat exchanger or reboiler. Other types of reboilers, such as internal reboilers, may also be used. The heat that is provided to the reboilers may be derived from any heat generated during the process that is integrated with the reboilers or from an external source such as another heat generating chemical process or a boiler. Although one reactor and one flasher are shown in the figures, additional reactors, flashers, condensers, heating elements, and other components may be used in various embodiments of the present invention. As will be recognized by those skilled in the art, various condensers, pumps, compressors, reboilers, drums, valves, connectors, separation vessels, etc., normally employed in carrying out chemical processes may also be combined and employed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As a practical matter, pressures from 10 kPa to 3000 kPa will generally be employed in these zones although in some embodiments subatmospheric pressures or superatmospheric pressures may be employed. Temperatures within the various zones will normally range between the boiling points of the composition removed as the distillate and the composition removed as the residue. As will be recognized by those skilled in the art, the temperature at a given location in an operating distillation column is dependent on the composition of the material at that location and the pressure of column. In addition, feed rates may vary depending on the size of the production process and, if described, may be generically referred to in terms of feed weight ratios.

The ethanol product produced by the process of the present invention may be an industrial grade ethanol comprising from 75 to 96 wt. % ethanol, e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on the total weight of the ethanol product. Exemplary finished ethanol compositional ranges are provided below in Table 12.

TABLE 12 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3 to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05 <0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05 n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferably contains very low amounts, e.g., less than 0.5 wt. %, of other alcohols, such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀ alcohols. In one embodiment, the amount of isopropanol in the finished ethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000 wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment, the finished ethanol composition is substantially free of acetaldehyde, optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5 wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanol product may be withdrawn as a stream from the water separation unit as discussed above. In such embodiments, the ethanol concentration of the ethanol product may be higher than indicated in Table 12, and preferably is greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greater than 99.5 wt. %. The ethanol product in this aspect preferably comprises less than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of the present invention may be used in a variety of applications including applications as fuels, solvents, chemical feedstocks, pharmaceutical products, cleansers, sanitizers, hydrogen transport or consumption. In fuel applications, the finished ethanol composition may be blended with gasoline for motor vehicles such as automobiles, boats and small piston engine aircraft. In non-fuel applications, the finished ethanol composition may be used as a solvent for toiletry and cosmetic preparations, detergents, disinfectants, coatings, inks, and pharmaceuticals. The finished ethanol composition may also be used as a processing solvent in manufacturing processes for medicinal products, food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemical feedstock to make other chemicals such as vinegar, ethyl acrylate, ethyl acetate, ethylene, glycol ethers, ethylamines, aldehydes, and higher alcohols, especially butanol. In the production of ethyl acetate, the finished ethanol composition may be esterified with acetic acid. In another application, the finished ethanol composition may be dehydrated to produce ethylene. Any known dehydration catalyst, such as zeolite catalysts or phosphotungstic acid catalysts, can be employed to dehydrate ethanol, as described in copending U.S. Pub. Nos. 2010/0030002 and 2010/0030001 and WO2010146332, the entire contents and disclosures of which are hereby incorporated by reference.

While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited herein and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention. 

We claim:
 1. A process for producing ethanol, comprising: vaporizing an acetic acid stream in a first vaporizer to form a first feed stream; reacting the first feed stream and a second feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product; separating at least a portion of the crude ethanol product in one or more columns to produce ethanol and a liquid recycle stream comprising ethyl acetate, wherein the liquid recycle stream comprises less than 600 wppm acetic acid; and vaporizing the liquid recycle stream in a second vaporizer to form the second feed stream.
 2. The process of claim 1, wherein the first feed stream is fed to the at least one reactor separately from the second feed stream.
 3. The process of claim 1, wherein hydrogen is fed to the first vaporizer and/or the second vaporizer.
 4. The process of claim 1, wherein the first vaporizer operates at a temperature from 20° C. to 300° C.
 5. The process of claim 1, wherein the second vaporizer operates at a temperature from 20° C. to 300° C.
 6. The process of claim 1, wherein the first vaporizer operates at a pressure from 10 kPa to 3000 kPa.
 7. The process of claim 1, wherein the second vaporizer operates at a pressure from 10 kPa to 3000 kPa.
 8. The process of claim 1, wherein the first vaporizer is constructed from a corrosion resistant material.
 9. The process of claim 1, wherein the second vaporizer is constructed from a different material than the first vaporizer.
 10. The process of claim 1, wherein the second vaporizer forms a blowdown stream and further wherein the mass ratio of the second feed stream to blowdown stream is from 6:1 to 500:1.
 11. The process of claim 1, wherein the liquid recycle stream further comprises ethanol and acetaldehyde.
 12. The process of claim 1, wherein the liquid recycle stream is substantially free of acetic acid.
 13. A process for producing ethanol, comprising: vaporizing an acetic acid stream in a first vaporizer to form a first feed stream; reacting the first feed stream and a second feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product; separating at least a portion of the crude ethanol product in a first distillation column to yield a first residue comprising acetic acid and a first distillate comprising ethanol, ethyl acetate, and water; separating a portion of the first distillate in the second distillation column to yield a second residue comprising ethanol and water and a second distillate comprising ethyl acetate, wherein the liquid recycle stream comprises less than 600 wppm acetic acid; and vaporizing the second distillate in a second vaporizer to form the second feed stream.
 14. The process of claim 13, further comprising separating a portion of the second residue in a third distillation column to yield a third residue comprising water and a third distillate comprising ethanol.
 15. The process of claim 13, further comprising separating a portion of the second distillate in a fourth distillation column to yield a fourth residue comprising ethyl acetate and a fourth distillate comprising acetaldehyde.
 16. The process of claim 13, further comprising vaporizing the fourth distillate in the second vaporizer to form the second feed stream.
 17. A process for producing ethanol, comprising: vaporizing an acetic acid stream in a first vaporizer to form a first feed stream; reacting the first feed stream and a second feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product; separating at least a portion of the crude ethanol product in a first distillation column to yield a first residue comprising acetic acid and a first distillate comprising ethanol, ethyl acetate, and water; removing water from at least a portion of the first distillate to yield an ethanol mixture stream comprising less than 10 wt. % water; separating a portion of the ethanol mixture stream in a second distillation column to yield a second residue comprising ethanol and a second distillate comprising ethyl acetate, wherein the liquid recycle stream comprises less than 600 wppm acetic acid; and vaporizing the second distillate in a second vaporizer to form the second feed stream.
 18. A process for producing ethanol, comprising: vaporizing an acetic acid stream in a first vaporizer to form a first feed stream; reacting the first feed stream and a second feed stream in at least one reactor in the presence of a catalyst to form a crude ethanol product; separating a portion of the crude ethanol product in a first distillation column to yield a first distillate comprising ethyl acetate and acetaldehyde, and a first residue comprising ethanol, acetic acid, water, or mixtures thereof; separating a portion of the first residue in a second distillation column to yield a second residue comprising acetic acid and water and a second distillate comprising ethanol and ethyl acetate; separating a portion of the second distillate in a third distillation column to yield a third residue comprising ethanol and a third distillate comprising ethyl acetate, wherein the liquid recycle stream comprises less than 600 wppm acetic acid; and vaporizing at least one of the first distillate or third distillate in a second vaporizer to form the second feed stream.
 19. The process of claim 18, wherein the first feed stream is fed to the at least one reactor separately from the second feed stream.
 20. The process of claim 18, wherein the third distillate is introduced into the first distillation column.
 21. The process of claim 18, further comprising removing water from at least a portion of the second distillate using a water removal unit selected from the group consisting of adsorption unit, membrane, molecular sieves, extractive column distillation, or a combination thereof. 